Fortinet FortiGate troubleshooting: following a packet, sessions, resources and VPN diagnostics
How FortiOS documents troubleshooting: define the problem and compare against a baseline, then follow the traffic with the packet sniffer, debug flow, the session table and the routing table. Then the problems the guide covers most: conserve mode and high CPU, FortiGuard updates that stop, and IPsec tunnels that won't come up, read from event logs and diagnose commands.
- Level
- Advanced
- Length
- About 55 minutes
- Contents
- 3 lessons · 1 video · final exam
- Status
- Published · updated 2 Oct 2026
- Fortinet FortiGate
Skills you'll practise
- Define a FortiGate problem using Fortinet's questions (what changed, scope, can it be reproduced) and a recorded baseline
- Run a filtered packet sniffer and a debug flow trace and read which route, policy and NAT a connection used
- Use the session table and routing table to confirm or rule out the FortiGate as the cause
- Recognise conserve mode and high CPU and explain what the fail-open settings do to traffic
- Work through Fortinet's FortiGuard update checklist and identify the failing step
- Tell from IPsec event logs and diagnose output whether phase 1 or phase 2 is failing
Course outline
- 1.FortiGate troubleshooting: follow the packetVideo · 2 min
- 2.A method and a baseline before the first commandLesson · 16 min
- 3.Following a packet: sniffer, debug flow, sessions and routesLesson · 20 min
- 4.Resources, FortiGuard and IPsec VPNLesson · 19 min
- 5.Fortinet FortiGate troubleshooting: following a packet, sessions, resources and VPN diagnostics: knowledge checkKnowledge check · 16 questions
- 6.Final exam10 questions · passing it completes the course, so people who already know the material can test out
Sources it draws on
The lessons and questions are written from these references, so learners can go back to the original.
- FortiOS Administration Guide: Troubleshooting methodologies
- FortiOS Administration Guide: Troubleshooting scenarios
- FortiOS Administration Guide: Running the TAC report
- FortiOS Administration Guide: Verifying the correct firewall policy is being used
- FortiOS Administration Guide: Performing a sniffer trace or packet capture
- FortiOS Administration Guide: Debugging the packet flow
- FortiOS Administration Guide: Using the debug flow tool
- FortiOS Administration Guide: Using a session table
- FortiOS Administration Guide: Verifying routing table contents in NAT mode
- FortiOS Administration Guide: Verifying the correct route is being used
- FortiOS Administration Guide: Running ping and traceroute
- FortiOS Administration Guide: Conserve mode
- FortiOS Administration Guide: Troubleshooting high CPU usage
- FortiOS Administration Guide: Verifying connectivity to FortiGuard
- FortiOS Administration Guide: Troubleshooting process for FortiGuard updates
And 3 more.
See it with your own jobs and topics
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